Over the last decade or so, many commercial and governmental entities have installed communication networks in order to allow their employees access various network resources. To improve efficiency and to support mobility, many wireless access enhancements have been added to local, personal, and wide area networks. Based on these enhancements, Wireless Local Area Networks (WLANs), Personal Area Networks (PANs) and Wide Area Networks (WLANs) have been and continue to be utilized by more and more users.
For instance, a WLAN supports communications between a number of wireless devices without any required line of sight for such communications. In current network configurations, multiple Access Points (APs) are connected using a distribution system, which may be a wireless or wired network, such as an Ethernet network for example, and each AP operates as a relay station by supporting communications between resources of the distribution system and wireless stations (STAs). STAs are fixed or mobile wireless devices, where the mobile devices enable users to alter their physical locations (e.g. roam), but still communicate over the network.
In wireless networks, “roaming” refers to the ability of a STA to move from one AP coverage area to another without any interruption in service or loss in connectivity. Apart from basic connectivity, it is important to maintain the same Quality of Service (QoS) for some applications such as voice and video, when a STA roams from one AP to another. Currently, when a STA wants to roam or associate with an AP, there are two primary methods that can be followed in order to assist the STA in making roaming decisions in compliance with the network's admission control constraints. “Admission control” is a network QoS procedure that is used to determine how bandwidth and latency are allocated to streams with various requirements. Admission control schemes are normally implemented at the APs to control the traffic entering the network.
For this first method, an AP periodically broadcasts load information, such as the number of stations associated with that AP or the total medium time available for example, as part of the beacons. However, this load information is unreliable because it does not provide an accurate representation of local constraints and other administrative policies. The granularity of aggregate medium time advertised in a load element is also insufficient for the STA to make appropriate roaming decisions based on QoS requirements, as it does not indicate the medium time per priority or access category. In addition, the AP may not update all the information contained in these periodic frames accurately before every transmission.
The second method involves associating to an AP, performing any necessary authentication and then negotiating QoS, such as using the ADDTS (ADD TSPEC) request. The AP may reject such a request after association and authentication, using a response message such as an Add Traffic Stream (ADDTS) response frame. When the request is rejected, the STA roams to another AP to restart the association and authentication process. While the first method is unreliable, the second method features high overhead because the STA needs to associate and possibly authenticate with the AP before making roaming decisions based on the inability to support requested QoS at the AP.
Moreover, after the acceptance of a STA's QoS request at the AP followed by the association of the STA, if the AP wants to re-adjust the QoS based on changes in local constraints or the RF environment or to allow an emergency call for a Voice Over Internet Protocol (VoIP) system, the AP has no graceful mechanism to modify an existing reservation. The AP has to actually disconnect the STA or delete the reservation or degrade the quality of the existing connections without an explicit notification to the STA in order to modify an existing reservation.